1. Field of the Invention
The present invention relates to network search in a wireless communication system. More particularly, the present invention relates to a method and apparatus of searching for an operator network and selecting the operator network by background searching and network selection in an environment to which multiple Radio Access Technologies (RATs) are applied.
2. Description of the Related Art
A Public Land Mobile Network (PLMN) is a mobile communication network configured generally with Base Stations (BSs) each managing one or more cells, a subscriber server, and a gateway. Mobile communication operators that provide mobile communication services have unique PLMN Identifiers (IDs) and a wireless terminal identifies the mobile communication operator and RAT of a mobile communication network to which a BS belongs by a PLMN ID received from the BS. Different mobile communication operators provide mobile communication services in different frequency bands. For example, RATs include 3rd Generation (3G) technologies such as Global System for Mobile communications (GSM), Code Division Multiple Access (CDMA), Wideband CDMA (WCDMA), Universal Mobile Telecommunications System (UMTS) and 4G technologies such as Long-Term Evolution (LTE), and the like.
To receive a mobile communication service, a wireless terminal is registered to a Home PLMN (HPLMN) of a specific mobile communication operator. If the wireless terminal supports roaming, the wireless terminal may receive a telephony service or a data communication service from a PLMN of another mobile communication operator other than the home PLMN. The network belonging to a different service provider (e.g., the other mobile communication operator) and visited by the wireless terminal visits is called a Visited PLMN (VPLMN).
In the European Telecommunication Standards Institute (ETSI) or 3rd Generation Partnership Project (3GPP), it is regulated that when a wireless terminal is located in a VPLMN, the wireless terminal searches for an HPLMN during a predetermined scanning time. In other words, when the wireless terminal receives a service in the VPLMN, a scanning timer of the wireless terminal (e.g., set to 2 minutes) starts and upon expiration of the scanning timer, the wireless terminal searches adjacent PLMNs for the HPLMN. In addition, the wireless terminal may search PLMNs in response to a manual manipulation from a user.
In most cases, PLMN searching progresses in the background during a time period in which the wireless terminal does not exchange signals with the current network, without interrupting an on-going task. When the wireless terminal supports multiple RATs, the wireless terminal should search PLMNs over each RAT, switching from one RAT to another RAT. If PLMN searching is not performed rapidly and accurately, the wireless terminal may continue receiving the service from the VPLMN despite the existence of a nearby BS of the HPLMN, thereby performing an unnecessary PLMN search procedure.
Accordingly, there exists a need for efficiently performing a background PLMN search procedure in a wireless terminal.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.